Page 35 - 新思维数学学生用书7 样章

2 Expressions, formulae and equations

4 Write an expression for the answer to each of these.

a Dravid has x DVDs. He buys six more.
How many DVDs does Dravid now have?
b Molly is m years old and Barney is b years old.
What is the total of their ages?
c Ted can store g photographs on one memory card.

How many photographs can he store on three memory
cards of the same size?

Think like a mathematician

5 Discuss in pairs or groups.

How would you write an expression for each of these?
a I think of a number x. I multiply the number by 6, then add 1.
b I think of a number x. I multiply the number by 4, then subtract 9.

c I think of a number x. I divide the number by 6, then subtract 1.
d I think of a number x. I divide the number by 2, then add 7.
e I think of a number x. I multiply the number by 2, then subtract the result from 25.

6 Maliha thinks of a number, y.

a Write an expression for the number Maliha gets when she:
i multiplies the number by 3
ii divides the number by 2 Tip

iii multiplies the number by 4, then adds 1 For part iii, if my number
iv multiplies the number by 2, then subtracts 5 is 5, I need to work out
v multiplies the number by 5, then subtracts the 4 × 5 + 1 = 20 + 1 = 21.
result from 52 Four times my number is 20,

vi divides the number by 4, then adds 3 and 20 add 1 equals 21.
b Check that your expressions are correct by So, my expression is 4y + 1.
replacing the y with a number.

Activity 2.1

Work with a partner to take it in turns to make up an ‘I think of a number’ question,
like those in Question 5.
For example, ‘I think of a number. I multiply by 3, then subtract 2.’

Your partner must write down the expression correctly, using a letter of their choice.
Check that their expression is correct. If it is correct, then your partner scores 1 point.
Do this five times each, then check your scores.

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